Service-Oriented Advanced Metering Infrastructure for Smart Grids

Transcription

1 Journal of Energy and Power Engineering 5 (2011) Service-Oriented Advanced Metering Infrastructure for Smart Grids S. Chen 1, J.J. Lukkien 1 and L. Zhang 2 1. Department of Mathematics and Computer Science, Eindhoven University of Technology, Eindhoven 5600 MB, Netherlands 2. East-China Power Dispatching Center, East-China Grid Group Company, Shanghai , China Received: July 26, 2010 / Accepted: October 20, 2010 / Published: May 31, Abstract: Advanced Metering Infrastructure (AMI) enables smart grids to involve power consumers in the business process of power generation transmission, distribution and consumption. However, the participant of consumers challenges the current power systems with system integration and cooperation and security issues. In this paper, the authors introduce a service-oriented approach to AMI aiming at solving the intercommunication problem and meanwhile providing a trust and secure environment for smart grids. In this approach heterogeneous systems expose services to the network. System integration and cooperation are done through service composition. A generic service interfacing method is designed to develop standardized services for heterogeneous power systems. Moreover, role-based access control mechanism is used to guarantee the secure access to smart grids. With the seamless communication between consumers and power systems and among power systems themselves, this service-oriented AMI can associate consumers with actual system workload and furthermore support the intelligent running of power systems. Key words: Smart grids, AMI, service-oriented, generic interfacing, access control. 1. Introduction Smart grids advocate the participant of consumers in the power business process including power generation, transmission, distribution and consumption [1-3]. Through collecting consumers motivation, their monitoring result on delivered power quality, and feedback, power product providers and operators can shape their market models according to the real demand, dynamically distribute their power transmission, achieve network optimization, and provide high quality of service to their consumers. This requires smart grids must a) provide new functionality that enables the involvement of consumer, b) deal with the collaboration of heterogeneous systems including smart sensors, smart meter monitoring systems, various back-end power Corresponding author: S. Chen, Ph.D., assistant professor, research fields: sensor networks, components based architecture, security and resource management. shudong.chen@tue.nl. information systems (distribution system, accounting and billing system, etc.), c) guarantee the secure communication between consumer and back-end systems and that among back-end systems. In order to achieve these goals, Advanced Metering Infrastructure (AMI) is proposed which uses two-way communications, advanced sensors, and distributed computing to improve the efficiency, reliability and safety of power delivery and use [4, 5]. AMI has been national widely deployed including Italy, Sweden and Finland, etc. However, by the nature of distributed power transmission and distribution environment, power information systems consist of heterogeneous networks, performing communication using different communication protocols. Even in the same network there may exists heterogeneity between development languages, deployment hardware and system structures (database, I/O interface, etc.). Moreover, they are tightly coupled with the security distribution policy and horizontal segregation of networks. Some of them are

2 456 Service-Oriented Advanced Metering Infrastructure for Smart Grids even running individually. As a consequence, system interactions are rather difficult. Increasing deeply system integration, seamless communication, cost, and safety requirements of smart grids reveals the need for a flexible, reliable, reusable, as well as trustable architecture for AMI. Service-orient technology [6, 7] provides a solution to solve system cooperation in a distributed environment. Applications can be achieved through coordinating and connecting independent functional entities (services). Services expose well-defined interfaces to the network and are defined independent of hardware platforms, operating systems and programming languages. This makes it possible to interact in a uniform and universal way between services or systems. Therefore, in this paper, we propose a service-oriented AMI. We envisage a smart grids system as an environment in which functionalities are provided as scalable services. Users, which include power providers, operators and consumers, can simply interact with the system without knowing how to access and control these services. The service-oriented framework will support the interactions of services provided by heterogeneous systems where issues including security, cooperation, atomization, and dynamic adaptive will be considered. The remainder of this paper is organized as follows. In section 2 we describe the service-oriented AMI for smart grids followed with detailed design of the generic service interfacing method A_ITF and working principle of the role-based access control mechanism. In section 3 we analyze the feasibility of our design together with a tooling support A_MAP. Finally we summarize and conclude in section The Design of a Service-Oriented AMI 2.1 Service-Oriented AMI Different from the traditional power systems, a novel feature of smart grids is using AMI to setup the connection of power systems with their consumers. AMI grants consumers with capability to support the intelligent running of power systems. Customs can check the delivered power quality through monitoring the smart meters installed along the power transmission, distribution and user path. Under special circumstances, for instance, disturbing or theft happen, they can inform or be informed by the custom service center. They can specify their requirement based on actual requirements and available rate models. Moreover, their activities can be collected for power operators to make new energy marketing strategies. AMI also provides time stamped system information for the back-end system analysis. For instance, through reading smart meters, network performance will be monitored. Subsequently, alarm, dynamic dispatching and work load forecast can be achieved. Additionally, system self healing functionality can also be provided. Fig. 1 shows the service-oriented AMI design which includes a custom portal (load management system) and some example power systems. Functionalities of all the subsystems are represented as services. We also wrap the modules of existing power systems as services, for example, the smart meter reading will be done by calling distributed meter reading services running on smart meters. 2.2 Business Process Lifecycle in Service-Oriented AMI In a smart grids system, a business process, which is also called an application, is achieved through service coordination and connection. A power operator wants to add a new function to the smart grids system, for example, to let customers be informed with new power products and according rating model. To enable this, an orchestrator, on behalf of the operator, will follow the steps, depicted in Fig. 2 to construct such a business process then publish as an application in the system for later use. The lifecycle of a business process consists of the following phases: (1) Service development and deployment: a service provider exposes a set of functions in the form of a generic service to the network. (2) Service advertisement: when a new service is available, it makes its presence known to other services

3 Service-Oriented Advanced Metering Infrastructure for Smart Grids 457 Fig. 1 Service-oriented advanced metering infrastructure. Fig. 2 Lifecycle of a business process in service-oriented advanced metering infrastructure. on the network. If there is a repository service, it sends out the advertisement through broadcast or multicast. Services who are interested in this repository record this information and register themselves at this repository next. If there is no repository available, services broadcast themselves. (3) Realize an application: when there is a requirement of an application, an orchestrator is going to achieve it through service combination following the below steps. Service discovery: the orchestrator discovers required services. It sends out service queries and then receives a list of available services with required functionalities. Service binding: the orchestrator informs specific services to bind with each other in an order according to the application logic. During this process, the orchestrator checks the match between services, e.g.,

4 458 Service-Oriented Advanced Metering Infrastructure for Smart Grids the interfaces and the communication protocols. Service invocation: this is the stage where a service is connected and invoked after the application starts. A service is called directly by another service. Although control is still done by the orchestrator, as shown in steps 3.31 and 3.4, the orchestrator is no longer involved in service function invocation. Run time service management: during the application execution, in order to guarantee the overall performance, e.g., the throughput of a service and robustness of the whole system, services are monitored and managed about their availability and resource usage. (4) Service unbind: after the application finishes, the orchestrator orders services to disconnect from their bound services, clean up whatever state needs to be removed and relinquish the control which is implicitly transferred upon binding. 2.3 A_ITF: Generic Service Interfacing Services provided by the load management system and example power systems, e.g., on demand ordering service, demand response management service, are developed and exposed in a generic way, A_ITF, shown in Fig. 3, to enable the collaboration over a heterogeneous networking environment. Different from the existing Web Services [8] and UPnP [9] specifications, where services only contain interfaces which express services capabilities, A_ITF defines that interfaces of a service can be divided into two types: provided interface and required interface. Capabilities of a service are expressed as provided interfaces; capabilities a service needs for its work are specified as required interfaces. Service compositions are created by connecting (binding) these required and provided interfaces. Special interfaces are used to program the extra-functional aspects including security, management and discovery, but also the mentioned binding. Separate orchestrators are capable of searching services and connecting them to form applications; orchestrators can also expose themselves again as services. In this way, applications can be achieved by service collaboration. More importantly, services have the ability to search for the functionalities they require through the network. This can solve the problem that application logic is encapsulated within services and dramatically enhance the reusability of services and the flexibility of the system [10]. All published methods of a service are added to the function interface. A_ITF is designed to support two service advertisement mechanisms: the mediated way which is achieved through a repository and the immediate way when there is no repository available on the network. In an immediate discovery protocol, a service broadcasts advertisements and queries while it listens to messages of broadcasted advertisements and queries. In case a service requires some interfaces from other services, it keeps a list of these services when it receives the advertisement messages from them. A service can subscribe to the events generated by another service. The Event Generator provides methods to register and unregister event listeners, as well as a method to inform all registered event listeners of the occurrence of an event. The Event Listener interface provides a callback method that can be called by an event generator once subscribed events occur. The purpose of the binding interface is to bind a required interface of a service to another service that provides that matching function interface. 2.4 Role-Based Access Control In order to protect smart grids from malicious attack and protect the privacy of consumers, smart grids services can be added with security-related interfaces. Consequently, only authenticated users can access them. Service discovery, access, and collaboration all happen in a trustworthy environment. The security interface, illustrated in Fig. 4, is used for checking the identification and capability of a service user, which can be fetched from a ticket, to access a smart grids service. All activities including advertisement, discovery, access and collaboration can only be executed with carrying a valid ticket. Only authenticated users can access a service and

5 Service-Oriented Advanced Metering Infrastructure for Smart Grids 459 Fig. 3 Static view of A_ITF. Asymmetric cryptography [11] is used for communication secrecy. The cryptographic key pair for encryption and decryption is distributed by the CA. 3. Implementation and Analysis Fig. 4 A_ITF with security related interface. communication messages are encrypted. Due to the fact that power systems are distributed, a single-sign-on mechanism is supported by this security interface. Different access actions are granted to different service users according to their roles. For instance, a consumer has to show his ticket signed by a trusted third party Certificate Authorization (CA) and the system administrator can specify which access actions are permitted to different roles. In this way, each access to a service has to verify that it is authorized. Moreover, all exchanged messages in smart grids are encrypted. To address the feasibility of this service-oriented AMI, we have developed a tooling support, A_MAP, to wrap a deployment platform independent A_ITF service into a deployment platform specific service. Currently, to deploy a smart grids service in type of Web Service is supported. The structure of A_MAP is depicted in Fig. 5. Besides AMI, the proposed service-oriented design is suitable for other modules in smart grids including Advanced Distribution Operations (ADO), Advanced Transmission Operations (ATO) and Advanced Asset Management (AAM). With the flexibility provided by the generic service interfacing, real time simulation, distributed operation, network optimization can be achieved with low-cost.

6 460 Service-Oriented Advanced Metering Infrastructure for Smart Grids Fig. 5 A_MAP overview. 4. Conclusions This paper presents a service-oriented AMI for smart grids to solve the intercommunication problem of current power systems. System functionalities are wrapped as scalable smart grids services exposing generic interfaces defined by A_ITF. A mapping tool, A_MAP, is developed to wrap a deployment platform independent smart grids services as Web Services. It supports the seamless interactions of heterogeneous systems where issues including flexibility, reliability and security are considered. With achieved seamless communication, this service-oriented AMI can associate consumers with actual system workload, furthermore support the intelligent running of power systems and meanwhile providing a trust and secure environment for smart grids. Acknowledgments We thank Melissa Tjiong and Remi Bosman for their technical feedback at the design and implementation stages of this work. We also thank our anonymous reviewers for their invaluable feedback which helped in improving the quality of the paper. References [1] M.C. Kintner-Meyer, D.P. Chassin, L.D. Kannberg, R.G. Pratt, J.G. DeSteese, L.A. Schienbein, et al., GridWise: The benefits of a transformed energy system, Pacific Northwest National Laboratory under Contract with the United States Department of Energy, 2008, p. 25. [2] M. Amin, B.F. Wollenberg, Toward a smart grid: Power delivery for the 21st century, IEEE Power and Energy Magazine 3 (5) (2005) [3] Cisco Outlines Strategy for Highly Secure, Smart Grid Infrastructure, 2009, available online at: [4] B. Loeff, AMI Anatomy: Core Technologies in Advanced Metering, Ultrimetrics Newsletter (Automatic Meter Reading Association), 2008, available online at: [5] Rochester Gas and Electric Corporation and New York State Electric and Gas Company, Advanced Metering Infrastructure Overview and Plan, 2007, available online at: Filing.pdf. [6] A. Korostelev, J.J. Lukkien, J. Nesvadba, Y. Qian, QoS management in distributed service oriented systems, Parallel and distributed computing and networks, in: Proc of IASTED Int. Conf. on Parallel and Distributed Computing and Networks, Innsbruck, Austria, Feb., [7] S. Chen, W. Zhang, F. Ma, A cooperative computing platform for drug discovery and design, in: IEEE Service Computing Conference, 2004, pp [8] E. Cerami, Web Services Essentials: Distributed Applications with XML-RPC, SOAP, UDDI & WSDL, O Reilly, [9] UPnP Forum, UPnP Device Architecture, Version 1.0, available online at: ecture-v1.0.pdf, [10] S. Chen, J. Lukkien, R. Bosman, R. Verhoeven, A generic service interfacing approach for home networking, in: IEEE International Conference on Consumer Electronics, 2010, pp [11] R. Housley, W. Ford, W. Polk, D. Solo, Internet X.509 Public Key Infrastructure: Certificate and CRL Profile, available online at: